The present invention relates, in general, to semiconductor devices, and more particularly to variable capacitance semiconductor devices.
In the past, the semiconductor industry has utilized various structures and methods to implement variable capacitance semiconductor devices such as varactor diodes, tuning diodes, and varicaps. Typically, these variable capacitance devices are formed by diffusing a dopant into a semiconductor material to form a single P-N junction and making electrical contact to the diffused region. A reverse voltage is applied that forms a depletion region around the diffusion. This depletion region has a capacitance associated thereto. As the voltage is varied, the value of the capacitance also varies.
The present trend to very low operating voltage creates a need to have a variable capacitance device that has a large capacitance density variation for a small change in voltage (pf/micron.sup.2 /volt. Typically, prior art variable capacitance devices vary up to 1.times.10.sup.-4 pico-farad per square micron per volt.
Accordingly, it is desirable to have a variable capacitance semiconductor device that has a capacitance that varies rapidly for a small change in voltage, and that has a variable capacitance range of approximately three volts.